1. FIELD OF THE INVENTION
This invention relates to a high temperature, corrosive, resistant structure and method of fabrication thereof. More particularly, this invention is directed to a specimen containment tubular housing of a cartridge assembly for use in furnaces, the cartridge assembly tubular housing is produced by plasma spray or other material deposition technologies to provide a gradient or composite structure which is corrosive resistant and operable on earth or in space at very high temperatures.
2. DESCRIPTION OF RELATED ART
Sample containment cartridge assemblies usable in furnaces are known and typically contain or produce samples which must be subjected to very high furnace temperatures while being corrosive resistant to protect against sample leakage. Such assemblies typically include an outer housing in the form of a tube which encloses various components including a sample containment container.
Currently there are no single-material cartridge tubes for supporting corrosive sample materials in furnaces which satisfy the requirements for space furnaces operating between the temperature ranges of 1200.degree. C. (230.degree. F.) to 2000.degree. C. (3632.degree. F.) In addition, the fabrication of current cartridge tubes has been complicated and expensive, requiring numerous steps & different fabrication processes. Sample containment cartridges are often machined or drawn, then the ends are welded on and finally the cartridge is coated. Inconel 718 has been used for previous experiments operating at 1150.degree. C. (2102.degree. F.). To provide containment for experiments above 1200.degree. C., a variety of refractory metals (i.e., Re, W, Ta, Mo, and alloys Nb--TiHf, Mo-40%Re, W-25%Re, W--Ni), and mixtures thereof were considered to be usable. The term "refractory metals" as used herein refers to metals having a melting point above 1200.degree. C. While these metals provide adequate strength at these high temperatures, they tend to be less able to withstand high temperature oxidation or liquid metal corrosion should sample containment (quartz) rupture or leak molten semiconductor materials (i.e., GaAs, Ge, etc.). A variety of ceramic materials (BN, Sic, Al.sub.2 O.sub.3, Si.sub.3 N.sub.4, SiO.sub.2, ZrO.sub.2) and mixtures thereof are impervious to the aggressive attack of the molten semiconductors and provide a high service temperature. However, the ceramics are too brittle to be fabricated (high thermal gradients induce stress) and handled in very thin sections as required for some applications, such as cartridge tubes which are operable in space.
Vacuum plasma spray ("VPS") techniques are utilized in the preferred embodiment of the present invention for the formation of a ceramic and refractory metal composite structure unachievable by conventional methods. Likewise, vacuum plasma spray techniques are utilized for the formation of a refractory metal tubular member suitable for such cartridge tubes. For fabricating the composite structure, it is of interest to utilize the desirable properties of both materials while compensating for their weak points. The ceramics' high temperature capabilities and corrosion/oxidation resistance combined with the refractory metals' ductility and toughness leads to a very robust cartridge tube for high temperature containment.